The deacylation of esters is performed in various fields. For example, it is used in releasing a photographic reagent from a photographic reagent precursor to be used in a silver halide photographic material, or in releasing a protective group in the synthesis of medicines.
In the cleavage of esters, a hydrolyzing method using hydroxy ions (.sup..crclbar. OH) or hydrogen ions (H.sup..sym.) is usually employed. However, when a molecule contains two or more acyl groups and only one of them is to be selectively cleaved, or when a compound or a functional group which is likely to be deteriorated by an acid or alkali coexists, the conventional hydrolyzing method using an acid or alkali often cannot be applied. For this reason, several improved methods have been developed.
For example, a method using ammonia in water-containing methanol is described in Tetrahedron Letters, p. 4273 (1968). A method using a large excess of butylamine is described in Tetrahedron Letters, p. 2263 (1986). A method using methyl-lithium is described in Journal of Orqanic Chemistry, Vol. 44, p. 2053 (1979). In addition, details of a cleavage method of similar esters are described in, for example, J.F.W. McOMIE ed., Protective Groups in Organic Chemistry, Plenum Press (NY) (London) (1973) and T.W. Greene, Protective Groups in Organic Synthesis, Willey Interscience (NY) (1981).
Although the above improved methods are useful in some cases, all the deacylating agents used in the methods are grouped into the category of "high nucleophilic agent and strong base" and, therefore, inevitably suffer from disadvantages. For example, in the aminolysis method, a large excess of amines is needed (10 equivalents in the literature). Thus, when a molecule contains, for example, a carbonyl group, a Schiff base is readily formed, and when a readily releasable group, such as a halogen atom, is present, a substitution reaction and a releasing reaction occur competitively.
In recent years, a highly selective organic reaction under mild conditions (neutral conditions) has been greatly desired. In view of this need, the above improved methods are not always satisfactory; a method of selectively cleaving the ester group under mild conditions without adversely affecting other functional groups has not been developed.
N-methyl-.alpha.-dialkylaminoacetohydroxamic acid compounds are described in Tetrahedron Letters, No 8, pp. 643-646 (1974) and Tetrahedron Letters, Vol. 30, No. 2, pp. 207-210 (1989). However, immobilization of the compounds onto insoluble polymers has not been reported.